Gas curtain continuous chemical vapor deposition production of semiconductor bodies

ABSTRACT

Apparatus and process for producing electronic-grade semiconductor bodies are disclosed wherein continuously-pulled slim rod which can be formed in situ from the reaction of a seed crystal and a molten semiconductor material source, is pulled into and through a chemical vapor deposition chamber, having a gas curtain along the inner wall, the slim rod surface being preheated before entry into the deposition chamber where it is simultaneously exposed to focused heating and thermally decomposable gaseous compounds in order to provide suitable surface reaction conditions on the slim rod for the decomposition of the gaseous compounds which results in deposition growth upon the surface of the rod. Single crystal semiconductor bodies are produced according to the process by avoiding poly-growth conditions through the in situ continuously pulled virgin slim rod, preheating of the slim rod for entry into the chemical vapor deposition chamber wherein the rod is simultaneously heated or maintained at reaction temperature conditions while being exposed or contacted with elected thermally decomposable gaseous compounds and continuously drawn through the chemical vapor deposition chamber reaction zone resulting in an enlarged single crystal semiconductor body which is withdrawn continuously from the chemical vapor deposition chamber.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and process for continuouslygrowing semiconductor bodies resulting from chemical vapor depositionupon in situ produced seed rod. In another aspect the invention relatesto the continuous deposition of single crystal semiconductor bodies fromcontinuously pulled virgin slim rods formed in situ, heating of the slimrods to temperatures which provide suitable surface conditions forcontacting selected thermally decomposable gaseous compounds in achemical vapor deposition chamber having a gas curtain along the innerwall, followed by removal of the resulting single crystal semiconductorbody from the chamber.

In the semiconductor industry, it is common to deposit material from thegaseous state onto a substrate for the purpose of forming variouselectronic devices. In some applications the material deposition fromthe gas is the same material as that from which the substrate is formed,while in other instances it is a different material from that from whichthe substrate is formed. As an example of the former, in the growth ofsilicon by vapor deposition techniques, it is common to position anelongated silicon filament between two graphite electrodes each of whichextends through the end of a quartz container within which the filamentis placed. A potential is impressed across the graphite electrodescausing a current to flow through the filament. The resistance of thefilament to current flow elevates the temperature of the filament to atemperature generally in excess of about 1100° centigrade.

A gas stream, which comprises a mixture of trichlorosilane and hydrogenand/or other silanes is introduced into the quartz chamber and afterflowing along the longitudinal axis of the filament is withdrawn fromthe chamber. The gas stream, upon contacting the hot surface siliconfilament, will react to deposit polycrystalline silicon on the filament,thus increasing the diameter of the filament. The reaction of thetrichlorosilane and hydrogen may be generally illustrated by thefollowing simplified formula:

    SiHCl.sub.3 +H.sub.2 →Si+3 HCl

Gas flow through the quartz cylinder or reaction chamber is usuallycontinued for several hours to increase the diameter of the filament,which may be one-tenth inch in diameter upon commencement of thedeposition, to the diameter in excess of five inches. When the siliconrod has reached a desired diameter, the flow is terminated and the rodis removed from the reaction chamber. Material deposited on the siliconfilament will be polycrystalline and therefore must be zone melted toproduce a single crystalline material. Alternatively, the poly crystalrod may be melted in a crucible and a large single rod is "pulled" fromthe melt by way of a variety of apparatus such as a "Czochralski"puller.

In both commercially accepted methods of producing single crystalsilicon for the electronics industry, that is by float zone or byCzochralski, the single crystal rod which is drawn from a melt in bothcases is rotated and results from the pulling of the melt in the form ofthe single crystal rod. Such methods require considerable skilledtechnician monitoring as well as multiple furnaces requiring substantialenergy for operation. Even under the best conditions, frequently thecrystal is lost during the first stage which means that the rod beingpulled converts to a polysilicon growth zone; thus terminating thegrowth procedure of the rod. Such commercial methods of producing remeltsingle crystal silicon rod materials is costly in time and effort andfrequently produce irregularly shaped cylindrical rods requiringsubstantial premachining before slicing and conversion into wafers foruse in the electronics industry.

Recent developments in the semiconductor industry have created a growingdemand for low-cost single crystal silicon of extremely high purity,which is known as semiconductor grade silicon. Semiconductor gradesilicon is used in the manufacture of semiconductor devices, such astransistors, rectifiers, solar cells, and the like. Processes are in usein the prior art producing single crystal silicon through the remeltingof polycrystalline semiconductor grade silicon.

The prior art processes have demonstrated the technical and economicfeasibility of producing high purity polycrystalline silicon ofsemiconductor quality by hydrogen reduction of silicon halides. Allcommercial semiconductor polycrystalline silicon presently beingmanufactured through chemical vapor deposition processes employ hydrogenreduction of dichlorosilane or trichlorosilane and the deposition ofsilicon on electrically heated silicon filament substrate.

This method relates to a method for producing high purity silicon orother semiconductor materials primarily for semiconductor device useand, in particular, to an improvement of the Siemens' process asdescribed by Gutsche, Reuschel, and Schweickert in U.S. Pat. No.3,011,877 and by Gutsche in U.S. Pat. No. 3,042,497. According to theseprior art patents, elemental silicon is obtained in the form ofcylindrical rods of high purity by decomposing silicon halides from thegas phase at a hot surface of the purified silicon filament, thepreferred halides being the chlorides, silicon tetrachloride and silicontrichloride. These compounds become increasingly unstable attemperatures above 800° C. and decompose in two ways: (1) Afteradsorption on a hot surface which can provide a substrate forheterogeneous nucleation, for example, when the silicon halideconcentration in the gas phase is kept relatively low by adding hydrogenas a diluent, the hydrogen also acts as a reducing agent; (2) in thecase of high halide concentration in the gas phase, homogeneousnucleation occurs and the resulting silicon forms a dust of extremelyfine particle size which is unsuitable for further processing.Heterogeneous nucleation hence silicon deposition starts at about 800°C. and extends to the melting point of silicon at 1420° C. Since thedeposition is beneficial only on the substrate, the inner walls of thedecomposition chamber must not reach temperatures near 800° C.

On the other hand, the deposition chamber wall temperature must not bemuch lower than about 500° C. because a cold wall is an effectiveheatsink and can easily overtax the ability of the electronic currentpassage through the substrate filament to maintain the 1150° to 1200° C.surface temperature needed to have the desired deposition on thefilament. Increasing the current through the substrate is not possibleas a consequence of the negative temperature coefficient of resistivityin silicon which causes the electronic current to flow preferentiallythrough the center of the cross section of the filament creating andmaintaining thus an overheated core. Filaments with surface temperaturesof over 1300° C. for example, have usually a molten core. As oneembodiment of U.S. Pat. No. 3,042,497 describes, the wall temperaturecan be effectively controlled by varying the amount and speed of the aircirculation over the outside of the decomposition chamber. However, asthe deposition progresses, the filament grows into rods of great weight,diameter and surface area which gives off radiant energy at least 10% ofwhich is absorbed by the quartz wall where the wall is absolutely clear.Much more energy is absorbed when the quartz does not transmit readilybecause of flaws within the quartz wall or just a general roughness ofthe quartz surface. Experience has indicated that the cooling air alonecannot satisfactorily solve the overall needs of silicon chemicaldecomposition chambers.

Epitaxially grown single crystal silicon by chemical vapor deposition(CVD) has been known since the early 1960's. It is also known to utilizevolatile acceptor or donor impurity precursors during growth processingof silicon; thus leading to the formation electricallyactive regions,bounded by junctions of varying thicknesses, carrier concentrations, andjunction profiles. Vapor substrate growth systems are quite general andin principle applicable to systems in which are provided pertinentkinetic and thermodynamic conditions of satisfactory balance.

The growth of single crystal silicon from the vapor phase is dependenton several important parameters, all of which interreact with each otherto some degree. These parameters can be described in part, for example,as substrate surface crystalographic orientation, the chemical system,reaction variables, such as concentration, pressure, temperaturemodification, and the appropriate kinetic and thermodynamic factors. Avariety of reaction systems have been investigated; however, all havethe common feature that a hot single crystal surface is exposed to anatmosphere which is thermal and/or chemical interreaction is capable ofproducing silicon atoms on a hot surface. The mechanism of thesilicon-forming reaction is a function of the temperature of thesubstrate.

In addition to known CVD epitaxially-grown silicon, epitaxial CVDprocesses using trichlorosilane have been demonstrated to achieveconversion yields of 50% or better and that single crystal depositiondoes occur at linear growth rates. It is further known that p-njunctions with theoretical I-V characteristics have been grown by CVDindicating the superiority of CVD crystal silicon over melt grownsilicon. However, practical application of chemical vapor deposition tothe preparation of single crystal semiconductor bodies has not beenextended to the preparation of rod shaped bodies but has been limited tothe preparation of thin epitaxial films on substrate in wafer form. Allattempts at preparing thick, i.e. more than a few thousandths of an inchsingle crystal bodies, have failed because of the unavailability ofadequate methods to provide and/or maintain an absolutelycontamination-free surface on the substrate seed and othermechanical-chemical problems. Similarly, all attempts at preparing rodshaped bulk single crystal bodies on electrically heated single crystalfilaments consisting of the same material have failed, mainly because ofthe unresolved difficulties with preparing and maintaining an absolutelycontamination-free substrate seed surface. In addition all previousattempts at developing processes for the direct deposition of rod-shapedsingle crystal bodies, energy applications have failed since directelectrical means were insufficient to provide the temperature uniformityessential to deposit a flawless single crystal body of homogeneouscomposition. Both a perfect single crystal structure and homogeneouschemical composition are conditions without which a semiconductor deviceconstructed by means of that single crystal body will not functionproperly.

SUMMARY OF THE INVENTION

To overcome the difficulties cited above, the invention provides aprocess and apparatus for preparing electronic grade semiconductorbodies from continuously pulled slim rod formed in situ from thereaction of a seed crystal and a molten semiconductor material source,pulled into and through a chemical vapor deposition chamber having aninternal gas curtain directed along the chamber walls. The invention ispredicated upon the use of an interior cooled wall curtain or coolingchamber walls as well as prohibiting reactor gas from making contactwith the chamber walls. Rather than use of an external gas such as airto regulate the chamber wall temperature, it is proposed to use part orall of the process gas to cool the inner wall directly; thus creating afluid or gas curtain. Such an arrangement would not only provideeffective cooling but could also preheat the process gas, thus reducingenergy loss due to radiation, convection and conduction which occursthrough an externally cooled chamber wall.

The in situ produced seed rod which is continuously drawn into andthrough the chemical vapor deposition chamber, heated before entry intothe chamber, and simultaneously exposed to further heating and selectedthermally decomposable gaseous compounds resulting in deposition growthof the body while the apparatus and methodology of the inventionsubstantially prohibits unwanted thermal deposition upon the innerchamber walls.

The high speed gas flow along the inner wall provides an effective gascurtain which prevents reactive gas from reaching the chamber wallsurface; thus avoiding deposits on the wall. This consideration shouldprove particularly useful in the case of silicon, when silane ormixtures of silicon halides with silane is used. Such mixtures of silaneand silicon halides reach deposition temperatures at approximately 400°C. In either case using silicon halides or mixtures of silane andsilicon halides, a fast well directed flow of process gas or hydrogen orinert gas taken from Group VIII A of the periodic chart along thedecomposition chamber wall in the amounts needed for dilution of thesilicon compound gases used, prevents silicon deposition on the walls.

In accordance with the principles of the invention, the CVD approach wasdirected to bulk single crystal operation. Such an approach would notonly eliminate the need for melt processing but also has the potentialfor producing a much improved product. The present apparatus utilized inthe standard Siemens' process decomposer employing two or morefree-standing filaments or slim rods providing substrate surfaces isinappropriate for the present invention since this apparatus is unsuitedfor the purpose of growing single crystals. While in the epitaxialprocess, major emphasis is placed in providing temperatures as uniformas possible across each substrate as well as from "wafer-to-wafer", nosuch temperature control has been achieved in the case of silicon singlecrystal, i.e. also called hex rod production. As a consequence of thenegative resistivity coefficient of silicon, all current heated siliconis hottest on the inside. Temperature differentials between the surfaceand the core of silicon bodies of as much as 120 degrees centigrade havebeen observed. The core begins to melt when the surface temperaturesreach approximately 1300° C. Also the flat areas of "hex rods" arealways hotter ( 10° to 50° C.) than the corners and the flat areasfacing another rod can be 10 to 50 degrees hotter than the "flat" facingoutside, i.e. the cooler decomposer wall. These large temperaturegradients naturally lead to thermal stress and lineage arrangement ofthe excessive dislocation generation.

Chemical vapor deposition chambers whether according to the continuousCVD process of the present invention or the Siemens' type decomposerprocesses for producing polysilicon share a common problem, that is,wall deposition coatings. Such wall depositions are undesirable sincecoatings force abortion of the process run because wall coatings preventmeasurement of substrate temperature in the case of Siemens' decomposerswhich is taken by optical pyrometer and in addition substantial depositsof silicon on the quartz decomposer wall tend to break the latterbecause of the difference in thermal expansion. Wall deposits areusually less dense than the filament deposits and tend to flaking. Theseflakes lodge on the filaments and result there in undesirable,irregular, sometimes dendritic growths which render the materialunsuitable for further processing. Even thin wall coatings react withthe quartz, actually etch quartz as shown on the following schematic.

    Si+SiO.sub.2 →2SiO␣

and strongly accelerate the devitrification of the fused quartz whichthen becomes opaque and must be at least partially remelted for the nextrun to clear up the crystallized layer. This is an interruptive andcostly maintenance problem. By eliminating wall deposits through thepresent invention, a substantial improvement in the preparation of highpurity silicon by continuous chemical vapor deposition can be achieved.The methodology and apparatus according to the invention or continuouschemical vapor deposition with silicon is even more sensitive to therequirements of an opaque chamber wall because of the focused externalheating means utilized in one embodiment of the invention.

The starting slim rod surface in prior efforts is usually chemicallyetched, a condition which has been proven to be particularly poor forgood epitaxial growth and all attempts to vapor etch the slim rod inhydrogen or hydrochloric acid did actually clean the decomposer insidewhich resulted in the deposition of varying impure "skins" on the slimrod. The initial deposit always showed a deep dip in resistivity as wellas a tell-tale ring when cross sections were treated with preferentialetches. This direct layer next to the original slim rod has always leadto what came to be believed "inevitable" chevron growth, i.e., stackingfault originated polycrystalline inserts in the otherwise single crystal"hex" rod. What is overcome by the present invention are theshortcomings mentioned in the two previous paragraphs by employing acontinuous feed of slim rod which has an as-pulled, "virgin" surfaceinto a tubular decomposer chamber. While slowly moving through thedecomposer chamber, the slim rod is uniformly heated by focused heatingmeans having a concentrated heat flux to the center line of thedecomposer chamber which is also the center line of the slim rod and thegrowing semiconductor body. Part of the necessary heat will be suppliedto the slim rod by passing a current through it, specifically during thepreheat stage before the slim rod is introduced into the decomposerchamber.

The apparatus and process according to the invention produceselectronic-grade semiconductor bodies, specifically the invention isdirected in part to electronicgrade semiconductor single crystalmaterials, for example, silicon. Following the single crystal siliconaspect of the invention, a slim rod pulling chamber is provided whereina virgin silicon slim rod is formed in situ from the reaction of theseed crystal and a molten silicon material source with the slim rodbeing pulled from the growth chamber through a communication zone of thegrowth chamber with a chemical vapor deposition chamber wherein the slimrod surface which has been preheated in the growth chamber issimultaneously exposed to focused heating and thermally decomposablesilicon containing gaseous compounds. The apparatus according to theinvention is designed specifically for single crystal growth as opposedto the Siemens' decomposer chambers as discussed hereinabove; thereforethe apparatus according to the invention is directed to provide a virginsilicon slim rod under suitable conditions for producing the mostdesirable equilibrium reaction flow of the thermal decomposition ofsilicon containing gaseous compounds with the result of single crystalsilicon being deposited and grown on the slim rod as the slim rod iscontinuously pulled through the chemical vapor deposition chamber.Single crystal silicon vapor deposition is a very complex process. Thepresent invention has utilized apparatus and methods which are basedupon identification and quantification of conditions necessary toproduce excellent quality single crystal silicon as the result ofintelligently controlling various variables in the process. Unlike muchof today's methods in producing single crystal silicon, which depends ingood part upon trial and error approaches, the present invention isbased on the proper approach of qualifying conditions under which goodsingle crystal silicon body can be produced through the direct thermaldecomposition of elected silanes and halogenated silanes. Favorablesilicon deposition conditions are greatly enhanced through the creationof a gas curtain along the chemical vapor deposition chamber inner wallsubstantially preventing the gaseous compounds, i.e. reaction gases fromreaching the wall. In another aspect, cool reaction gas can be utilizedas a curtain and recycled to the chamber at decomposition temperaturesthrough an entry means along the center of the chamber and body.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is an elevated somewhat schematic view of an apparatususeful in the practice of the invention wherein the gas curtain isprovided along the walls of the continuous chemical vapor depositionchamber in the practice of the continuous process according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a process and apparatus for depositingsemiconductor materials, such as elemental silicon, from a reaction gascapable of pyrolytically depositing the semiconductor materials on aheated, in situ drawn virgin seed rod under conditions which promotesingle crystal deposition rates allowing for continuous drawing of therod through the chemical vapor deposition chamber. A significantdeposition rate enhancement occurs through the utilization of a gascurtain along the chemical vapor deposition chamber inner walls whichcools the walls while substantially prohibiting contact with the wallsof the incoming hot reaction gases, i.e. silane and/or halogenatedsilanes which under the forced equilibrium conditions would deposit onthe walls or flake. The requirement of having transparent clean wallsaccording to the method of the invention, is critical in one embodimentwherein externally focused heat through the transparent walls isnecessary in order to achieve controlled continuous chemical vapordeposition upon the growing silicon rod.

The thermodynamics of a silicon-chlorine-hydrogen system are generallyunderstood. The equilibrium compositions are fully quantified; however,the kinetics of silicon chemical vapor deposition (CVD) are very poorlyunderstood and multiple reactions appear to occur. Quantitatively, it isknown that the deposition rate rises first rapidly with temperature, isthereafter less sensitive to temperature at high temperatures and mayeven drop with further increase in temperature within the upper limits.Mass transfer and heat transfer in silicon CVD systems utilizing radiantheating have not previously been well understood and continue to beevasive of exact quantification. Due to the complexity of the CVDprocess two specific goals were necessarily resolved through theinvention, that is, high direct deposition rates while avoiding walldeposition.

The single crystal silicon chemical vapor deposition process accordingto the invention can be simply described as growth of a single crystalfrom a mixture of gases containing silicon such as halogenated silanesand/or silane and hydrogen at elevated temperatures. Behind this simpledescription a number of complex phenomena remain for the most partunresolved. Chemical thermal dynamics establishes the maximum attainableyields which depends on temperature and initial molar ratios. Variousgas phase and gas/solid reactions are involved, the kinetics of whichdepend on temperature, gas composition, and crystal orientation.Absorption-desorption of reaction end products on crystal surfaces isalso temperature dependent as are the rates of and crystal growthnucleation. Finally, the gas composition and temperature on the crystalsurface are affected by the flow pattern in the reactor which determinesmass transport and heat transfer.

In the following description of the invention, the process will bedescribed on the basis of producing elemental, single crystal siliconfrom a reaction gas mixture, comprised of hydrogen, silanes, and/orhalogenated silanes, preferably trichlorosilane. However, this is forconvenience only and the invention may also be practiced with otherthermally decomposable semiconductor compounds capable of yieldingselected semiconductor materials. For silicon sources such astetrachlorosilane, tetrabromosilane, tribromosilane, for example, aswell as other suitable thermally decomposable compounds may be used.

The term "continuous" as used herein and in the claims is defined as thepulling of an in situ virgin slim rod from the pulling chamber directlyinto and through the chemical deposition chamber whether the pulling isabsolutely continuous or in stop and go motion. The concept "continuous"as defined herein is to illustrate the fact that the semiconductorbodies are produced on a virgin slim rod fashioned continuously andmoved through the chemical vapor deposition chamber without break in theproduction scheme, with finished product being drawn from the chemicalvapor deposition chamber either into the upper chamber storage area orinto the atmosphere where it can be scribed and broken or sawed andremoved from the continuously produced rod. The process according to theinvention can be continuous in motion or can be continuous withintermittent motion through the respective chambers. In another aspectthe continuous process can be defined as drawing the seed rod into andthrough the chemical vapor deposition chamber with a period of stopmotion for growth of the semiconductor body and thereafter removing thatrod segment from the chemical vapor deposition chamber whichsimultaneously loads the chamber with new virgin seed rod.

The in situ produced virgin slim rod or seed rod can be the result of aseed float-zone or Czochralski silicon melt source which is madeavailable in the pulling chamber. In the case of float-zone, thecontinuous supply rod can be fed through the bottom portion of thepulling chamber in a continuous mode depending upon the requirements forseed rod production as the seed rod is pulled into and through thechemical vapor deposition chamber. In addition the slim rod is heatedprior to entry into the chemical vapor deposition chamber and itspathway is clearly defined through a sleeve mechanism which is ofsufficient diameter to allow the slim rod to pass therethrough withouttouching. The restrictive nature of the sleeve and communicationpassageway between the pulling chamber and the chemical vapor depositionchamber permits open communication for passage of the slim rod; however,it does not permit substantial gas transfer between the two chambers.According to the invention a positive pressure exists in the pullingchamber which comprises hydrogen or helium or some other suitable inertgas which will not interfere with the reaction gas thermal decompositionprocess of the CVD chamber. This positive pressure permits, for example,hydrogen to enter into the CVD chamber in very small amounts which willnot interfere with the reaction gas thermodynamics or kinetics ofdepositing silicon upon the heated slim rod.

The pulling of a virgin silicon slim rod of single crystal compositionis necessary in order to insure elimination of many of the causes forpoly growth in a CVD chamber. For example, initially, commerciallypulled single crystal slim rods, or chemically etched or prepared byother known methods, have been found to contain sufficient surfacecontamination or defect problems which lead to substantial polyformation upon the decomposition of the reaction gases in the CVDchamber. It should be noted however that according to the invention thatthe process and apparatus as presented can always be utilized for theproduction of polycrystalline silicon if that result is desired. Infact, it may be highly desirable for the following reasons. The presentpoly requirement for removing the slim rod or filament from an externalslim rod puller to the reaction chamber thereby exposing the virginsurface of the slim rod to handling in an atmospheric environmentinevitably causes impurities from the environment as well as particularmatter to be lodged in the form of an absorbed layer of the surface.From this surface neither the adsorbed atomic or molecular species northe particulate matter can be removed completely by predeposition vaporetching. During the following deposition of silicon from the CVDreaction the first layer will therefore be impurity-rich and affected bynumerous point defects which will cause polycrystalline growth inselected areas.

It follows therefore that in the traditional Siemens' process for thepreparation of semiconductor grade polycrystal silicon in whichexternally prepared slim rods serve as substrate, there are alwayshighly contaminated initial layers with trapped impurities whichseverely limit the potential of the Siemens' process to prepare ultimatedegrees of purity of the product silicon. This means that the processand apparatus disclosed in this invention is also extremely useful inthe preparation of polycrystalline silicon rod of superior purity, forexample, as needed for float zone feed. The process and apparatus canalso be utilized for a variety of semiconductor body production whereinthe deposition material is acquired through thermal decomposition ofgaseous compounds. The above described processes are particularlyadvantageous when applied to silicon. The method, however, is alsoapplicable to other semiconductor substances which are required inextreme purity, and are preferred in monocrystalline form; for example,in the manufacture of electronic semiconductor devices such asrectifiers, transistors, solar cells, photo cells, and the like. Themethod is suited to the production of highly purified germanium, andsemiconducting compounds of elements from the third and fifth groups ofthe periodic system to form such compounds as BN, BP, BAs, BSb, AlN,AlP, AlAs, AlSb, GaP, GaAs, GaSb, InN, InP, InAs, InSb, and the like.The process is also utilizable for the meltless production of otherdesirable substances particularly metals and metals compounds havinghigh melting points.

Once the virgin slim rod which has been preheated and drawn into andthrough the CVD chamber the rod is simultaneously exposed to focusedheating and in the case of silicon, silicon-containing decomposablegaseous compounds. The CVD chamber is arranged in such a manner as toafford continuous focused heating in a geometrical manner on the rod forsubstantially the entire length of the chamber. The method of heatinghas to provide sufficient energy to maintain the substrate surfacetemperature between 1000° C. and 1300° C., preferably 1500° C.-1250° C.,at all times and has to provide sufficiently uniform heating to thesubstrate so that the surface temperature does not vary more than about±10° C., preferably ±5° C., or less, along the entire deposition area.

Various gas feed arrangements can be utilized in the CVD chamber withone preferred embodiment inclusive of a countercurrent flow of reactiongas as opposed to the continuous movement of the slim rod and/or growingbody. The process according to the invention does not require rotationof the slim rod or of the drawing body which is generally the case ofmodern remelt methods; however, if desired, rotation of the growing bodycould be utilized according to the invention when, for example, animprovement of deposition uniformity is desired.

In the continuous process and apparatus for producing semiconductorbodies from slim rod through the utilization of a CVD chamber, thewithdrawal of the grown body or of silicon hex rod can be achieved byvarious means. One suitable means is through a gas lock whichincorporates movement of the hexagonal body to a restricted zone whereinit first contacts one reactive gas jet thereafter followed by contactwith a vacuum zone and thirdly an inert gas jet. These variousgas-vacuum zones can be repeated, the number according to the need. Suchgas seal means are achievable because of the relatively low pressure ofthe reaction gas system within CVD reaction chamber. The gas seal meansalso permits various shaped articles, i.e. cylindrical, irregular shapedcylindrical and hexagonal configurations to pass through a restrictedmechanical barrier without touching the barrier. In addition, these gasseal means zones can be utilized for initial cooling of the growth bodyas it leaves the reaction chamber and enters into atmospheric conditionsor storage conditions. Once the growth body has been drawn for adistance somewhat removed from the CVD chamber and gas seal means in theatmosphere, the body can be scribed, snapped, broken or sawed from thecontinuously pulled growth body source, the separation depending ontemperature of the growth body at the point of separation and lack ofmechanical shock to the continuously growing body system.

In another embodiment of the invention, the growth body is pulled fromthe CVD chamber through a mechanically restricted zone which permitswithdrawal of the body without touching the walls of said zone with thebody being drawn into an expansion chamber comprised of, for example, abellows expansion chamber which permits the growth body to achievevarious lengths outside the CVD chamber depending upon the length of thebellows apparatus. One advantage of such a system permits the cool downof the rod to be achieved in controlled atmospheric conditions. Thebellows would necessitate eventual temporary shutdown of the continuousprocess; however, such shutdown would not necessarily contaminate thesystem for restart achieved by thermal build up and reaction gasintroduction to the CVD chamber after an inert gas purge. Here again theCVD chamber is at a relatively low pressure during operation andpositive pressure can be maintained between the CVD chamber and thebellows reception chamber during continuous growth and during shutdownremoval of the grown body.

In another version of the slim rod puller, reaction chamber, bellowsstorage chamber assembly, a gas seal means could be provided between thedeposition chamber and the bellows storage chamber thus eliminating theneed for any interruption of the deposition process during removal ofthe product rod from the bellows storage chamber.

Before discussing the various apparatus illustrated in the drawingswhich are useful for practicing the invention, it is to be noted that amain feature of the invention is to allow one to select specificdeposition rates at an optimum value and to maintain this value duringthe entire deposition process in a continuous mode. In that regard, itis desirable to select the deposition rate as large as possible, but inso doing to also insure that neither homogeneous nucleation of, forexample, silicon, in the free gas phase nor deposition of silicon on theinterior walls of the CVD chamber occurs. In addition the utilization ofa virgin silicon slim rod prepared in situ creates the best possibledeposition surface for creating single crystal silicon bodies.

The preferred embodiments of the apparatus and process to be employedfor the purpose of the invention are schematically illustrated in thedrawing.

In the FIGURE, a source feed rod of polycrystalline silicon 1 having adirect current connection 5 is automatically fed through means 3 inthrough seal means 7 into the virgin seed rod pulling chamber 9. Thedirect current connection 5 is utilized for resistive preheating of thevirgin seed rod or slim rod 19 before entry into the chemical vapordeposition chamber 23. The source rod seal means 7 can be of variousconstructions which allow longitudinal transport into a pressurizedchamber. The slim rod pulling chamber 9 is equipped with chamber inletgas facilities 11 which maintains a positive pressure upon the pullingchamber 9 utilizing, for example, hydrogen or helium or some othersuitable gas which is inert to the thermal decomposition reactions whichoccur in the CVD chamber 23. Pulling chamber 9 may be vented by outletmeans; however, the positive pressure should be maintained and theoutlet can be through the quartz sleeve 21.

The source feed rod 1 provides a source rod melt 17 through utilizationof a high energy heating coil 15, for example, similar to physicalconditions utilized in commercial float zone technology. The virgin slimrod 19 is produced through the action of a single crystal seed anddrawing of same from the source rod melt 17. The virgin slim rod 19 iscontinuously pulled from the pulling chamber 9 into and through the CVDchamber 23 through a communication zone between chambers 9 and 23comprised of a quartz sleeve 21 which serves the purpose of reducingtemperature loss of the CVD chamber and in combination with the positivepressure of the pulling chamber 9 prohibits process or reaction gas lossfrom CVD chamber 23. In addition, the quartz sleeve 21 in therestrictive communication zone between the two chambers prohibitscontact of the seed rod 19 with the process gas in the CVD chamber 23until ideal reaction conditions exist which occur upon entry into theCVD chamber 23 through the simultaneous focused heating from the radiantheat furnace 25 in combination with CVD chamber 23 transparent walls 27and contacting of the slim rod 19 with process gas from inlets 32. Theprocess gas inlets can be arranged in interior circular dispersion heads30 which encompass the growth rod and can enter the CVD chamber 23 atvarious points along the chamber walls. The reaction gas inlet 32 canalso be utilized in combination with tangential contact jets with thesilicon body 31 wherein multiple reaction gas inlets 32 are utilized incombination along the length of chamber 23. Gas curtain inlets 34 can bearranged in various positions along the chamber walls 23 wherein the gascurtain is guided upon entry through flow guides 36. The gas curtain canbe parallel to the flow of the reaction gas from, for example, thereaction feed head 30 or can be countercurrent to the reaction gas flow.A preferred embodiment is a countercurrent flow of the gas curtain tothat of the reaction gas flow, the reaction gas being fed toward thecenter of the chamber 23 while the gas curtain is fed into and directalong the inner wall of chamber 23.

The resulting hexagonal silicon body 31 increases in diameter as itproceeds through the CVD chamber 23 reaching a maximum rod diameter 33at the upper end portion of chamber 23. The continuous process and theapparatus according to the invention provide a gas seal means 37 at theupper end of chamber 23 which permits continuous drawing of the enlargedhexagonal body from the chamber without loss of process gas orcontamination of the CVD chamber. The continuous motion of the seed rodand the growth rod is achieved through automatic rod pulling means 39which are exterior to the CVD chamber 23.

Other embodiments of the invention which are not shown in the FIGUREwould be the utilization of an expansion type bellows chamber affixed tothe upper end of the chamber 23 which may or may not be in combinationwith a gas seal means 37.

In the following examples the invention is illustrated more fully withexperimental data wherein no wall deposits of silicon were observedthrough the conditions as set out in the Table below. The process gasesinclusive of hydrogen, tetrachlorosilane and trichloro-silane areindicated in units of liters per minute while a hydrogen blanket wasused in the examples, also shown in liters per minute flow. Thedeposition rate in microns per minute is also included and variesaccordingly with the variations and process gas content and hydrogenblanket flow.

                  TABLE                                                           ______________________________________                                                Process Gas    Hydrogen  Deposition                                   Example (l/min.)       Blanket   Rate                                         No.     H.sub.2 SiCl.sub.4                                                                           SiHCl.sub.3                                                                         (l/min.)                                                                              (microns/min.)                           ______________________________________                                        1       31.9    1.1    --    65      3.9                                      2       31.8    1.4    --    75      3.7                                      3       51.0    0.9    2.6   60      8.0                                      4       29.7    --     4.7   60      9.2                                      ______________________________________                                    

We claim:
 1. A continuous process for preparing bodies of semiconductormaterials comprising:(a) pulling a virgin slim rod in situ in a pullingchamber from the reaction of a seed crystal and molten semiconductormaterial source; (b) heating the slim rod to decomposition temperatureof gaseous compounds containing suitable semiconductor materials fordeposition upon the slim rod; (c) passing the heated slim rod into achemical vapor deposition chamber; (d) maintaining the slim rod at atemperature sufficient for decomposing the gaseous compounds whilecontacting the slim rod with the decomposable gaseous compounds duringthe slim rod's transport through the chemical vapor deposition chamber;(e) creating a gas curtain along the chemical vapor deposition chamberinner wall substantially preventing the gaseous compounds from reachingthe wall; (f) enlarging the slim rod as a result of thermaldecomposition of the gaseous compounds; and (g) pulling the resultingenlarged semiconductor body from the deposition chamber.
 2. Thecontinuous process according to claim 1 wherein the slim rod upon entryinto the chemical vapor deposition chamber and transport through thechamber is exposed to concentric, uniform heating through geometricallyfocusing heating means.
 3. The continuous process according to claim 2wherein the heating means is comprised of a radiant heat furnacesurrounding the chamber and focusing the heat onto the slim rod throughtransparent walls of the chamber.
 4. The continuous process according toclaim 2 wherein the slim rod is simultaneously exposed to the focusingheating means and the decomposable gaseous compounds.
 5. The continuousprocess according to claim 1 wherein the gas curtain is selected fromthe group consisting of hydrogen, helium, neon, argon, krypton, xenonand randon.
 6. The continuous process according to claim 1 wherein thegas curtain is comprised of a hydrogen curtain and the curtain isintroduced countercurrent to the decomposable gaseous compounds.
 7. Thecontinuous process according to claim 1 wherein a positive pressure ismaintained between the slim rod pulling chamber and the chemical vapordeposition chamber, the positive pressure creating a gas flow from thepulling chamber into the chemical vapor deposition chamber.
 8. Thecontinuous process according to claim 1 wherein the pulling chamber isprovided a continuous semiconductor materials source thus providing acontinuous slim rod source for the chemical vapor deposition chamber. 9.The process according to claim 1 wherein the continuous movement of theslim rod into and through the chemical vapor deposition chamber iscountercurrent to the decomposable gaseous compound flow.
 10. Thecontinuous process according to claim 1 wherein the resulting enlargedsemiconductor body exits the chemical vapor deposition chamber throughan exit means which provide cooling of the semiconductor body beforeentry into atmosphere storage zones.
 11. The continuous processaccording to claim 1 wherein the enlarged semiconductor body exits fromthe chemical vapor deposition chamber into an expandable chamber zonewhich is in communication with a chemical vapor deposition chamber. 12.A continuous process for preparing bodies of semiconductor materialcomprising:(a) pulling a virgin slim rod in situ in a pulling chamberfrom the float zone reaction of a seed crystal and molten semiconductormaterials source, the material source being continuously supplied; (b)heating the slim rod to decomposition temperature of gaseous compoundscontaining suitable semiconductor material for deposition upon the slimrod; (c) passing the heated slim rod through a communication zonebetween the pulling chamber and the chemical vapor deposition chamber;(d) maintaining the slim rod at a temperature sufficient for decomposingthe gaseous compounds through focused radiant heat furnace means whilecontacting the slim rod countercurrently with the decomposable gaseouscompounds; (e) creating a gas curtain along the chemical vapordeposition chamber inner wall substantially preventing the gaseouscompounds from reaching the wall; (f) enlarging the slim rod diameter asa result of thermal decomposition of the gaseous compounds; and (g)pulling the resulting enlarged semiconductor body from the depositionchamber through gas lock and cooling means.
 13. A continuous process forpreparing bodies of single crystal silicon comprising:(a) pulling avirgin single crystal silicon slim rod in situ in a pulling chamber fromthe reaction of a seed crystal and a continuous source of moltensilicon; (b) heating the virgin slim rod to decomposition temperature ofgaseous silicon compounds which will thermally decompose upon the heatedslim rod; (c) passing the heated slim rod into a chemical vapordeposition chamber; (d) maintaining surface temperatures of the rod,from about 1,000° C. to about 1,300° C. through heat focusing means; (e)contacting the rod surfaces with a gas having the formula Si_(k) H_(m)X_(n) where k is a number from 1 to 2, m is a number of from 0 to 6, nis a number of from 0 to 6 and X is a halogen; (f) creating a gascurtain along the chemical vapor deposition chamber inner wallsubstantially preventing the gaseous compounds from reaching the wall;(g) depositing silicon on the single crystal rod surfaces as the rod ismoved through the chemical vapor deposition chamber; and (h) withdrawingthe resulting enlarged single crystal silicon body from the chemicalvapor deposition chamber.
 14. A continuous process according to claim 13wherein the thermally decomposing silicon deposits upon the singlecrystal seed rod forming a single crystal structure.
 15. A continuousprocess according to claim 13 wherein the thermally decomposing silicondeposits upon the single crystal seed rod forming a single crystalstructure having hexagonal surfaces.
 16. The continuous processaccording to claim 13 wherein the heated virgin slim rod is introducedinto the chemical vapor deposition chamber and simultaneously exposed tofocused heating and thermally decomposable gases of silicon containingcompounds resulting in the decomposition of single crystal siliconhaving the orientation and crystal lattice structure of the seed rod.17. The continuous process according to claim 13 wherein the gas curtainis comprised of a hydrogen curtain and the curtain is introducedcountercurrent to the decomposable gaseous compounds.
 18. A continuousprocess according to claim 13 wherein a positive pressure differentialexists between the pulling chamber and the chemical vapor depositionchamber resulting in a positive gas flow from the pulling chamber to thechemical vapor deposition chamber.
 19. The continuous process accordingto claim 18 wherein the gas forming the positive pressure from thepulling chamber to the chemical vapor deposition chamber is selectedfrom the group consisting of hydrogen, helium, neon, argon, krypton,xenon and radon.
 20. A continuous process according to claim 13 whereinthe molten silicon source is continually supplied through float-zonemeans.
 21. A continuous process according to claim 13 wherein the moltensilicon source is continuously supplied through Czochralski means. 22.The continuous process according to claim 13 wherein the thermallydecomposable silicon containing gaseous compounds are comprised oftrichlorosilane.
 23. A continuous process for preparing bodies ofpolysilicon comprising:(a) pulling one or more virgin silicon slim rodsin situ in a pulling chamber from the reaction of one or more seedcrystals and a continuous source of molten silicon; (b) preheating andintroducing the silicon slim rods into a chemical vapor depositionchamber; (c) simultaneously heating and contacting the introduced slimrods to decomposition temperature of silicon containing gaseouscompounds; (d) maintaining slim rods at a temperature sufficient fordecomposing silicon containing gaseous compounds while passing slim rodsthrough the chemical vapor deposition chamber; (e) creating a gascurtain along the chemical vapor deposition chamber inner wallsubstantially preventing the gaseous compounds from reaching the wall;(f) enlarging the slim rod's diameter as a result of thermaldecomposition of the silicon containing gaseous compounds; and (g)pulling the resulting enlarged polysilicon bodies from the chemicalvapor deposition chamber.
 24. Apparatus for continuous growth ofsemiconductor material bodies comprising:(a) a slim rod growth chamberhaving an upper end in communication with the vapor deposition chamberlower end through a narrowed passageway of sufficient diameter to allowpassage of the slim rod from the growth chamber into the chemical vapordeposition chamber without touching; the growth chamber in lower endcommunication with a continuous source of semiconductor feed rod whichprovides a melt source through high energy heating coil means; (b) awithdrawable pulling means extending downward through the chemical vapordeposition chamber and into the growth chamber; (c) growth chamber slimrod heating means; (d) geometrically focusing radiant furnacesurrounding the chemical vapor deposition chamber walls, the chamberwalls being transparent to the focused heat; (e) growth chamber enteringgas pressure source means; (f) reaction gas entering and exit means tothe chemical vapor deposition chamber; (g) gas entry flow guide meanswhich provide a gas curtain along the chemical vapor deposition chamberinner wall substantially preventing the gaseous compounds from reachingthe wall; and (h) exit means from the chemical vapor deposition chamberupper end comprised of a gas seal means.
 25. The apparatus contained inclaim 24 wherein the narrowed passageway providing communication betweenthe growth chamber and the chemical vapor deposition chamber iscomprised of a quartz sleeve.
 26. The apparatus according to claim 24wherein the growth chamber slim rod heating means is comprised ofresistive heating.
 27. The apparatus according to claim 24 wherein thechemical vapor deposition chamber upper end is comprised of an expansionmember permitting the semiconductor material body to be drawn upwardlyfrom the chemical vapor deposition chamber.
 28. The apparatus accordingto claim 24 wherein the gas curtain is introduced into the chemicalvapor deposition chamber through at least one entry guide meanscountercurrent to the reaction gas entry which provides central chamberflow along the semiconductor body.